Head and neck squamous cell carcinomas (HNSCCs) are a heterogeneous group of tumors that arise from the epithelium of the upper aerodigestive tract. HNSCC is the 6th most common malignancy in humans and is associated with high alcohol and tobacco use. Despite the tremendous improvements in surgery, radiotherapy and chemotherapy over the last decade, the prognosis for patients with head and neck SCC is more or less unchanged. This is because patients continue to die from metastatic disease at regional and distant sites. Improvement in patient survival requires an increased understanding of tumor metastasis so that aggressive tumors can be detected early in the disease process and targeted therapeutic interventions can be developed. Detection of local lymph node metastasis is pivotal for choosing appropriate treatment, especially for individuals diagnosed with HNSCC in the oral cavity or oropharynx (Pantel and Brakenhoff 2004). Most of these individuals have the primary tumor removed. Treatment of individuals clinically diagnosed with lymph node metastasis (N+ status) involves the additional surgical removal of a substantial portion of the neck, including all five local lymph node levels (radical neck dissection, RND). Upon histological examination of removed tissue, 10-20% of clinically diagnosed N+ individuals turn out to be metastasis-free (N0) (Woolgar 1999).
Clinical diagnosis of N0 status is even less accurate. Postoperative histological examination shows that approximately one-third of clinically diagnosed N0 individuals have metastasis-positive lymph nodes in the neck (Jones et al. 1993). Currently, there are several different strategies exist for treating diagnosed N0 individuals (Pillsbury and Clark 1997). In the “watch and wait” strategy, diagnosed N0 individuals do not undergo any neck dissection; this risks fatality by allowing overlooked metastases to spread further. Because the false-negative rate is very high, most clinics carry out neck surgery for all diagnosed N0 individuals. In these cases, a supra-myohyoid neck dissection (SOHND) is done, which removes the three upper lymph node levels (Robbins et al. 2002). SOHND is less appropriate than RND for N+ individuals falsely diagnosed as N0 and, moreover, is completely unnecessary for individuals correctly diagnosed as N0. Although SOHND is less rigorous than RND, the treatment causes disfigurement, long-term discomfort and pain and can lead to additional complications such as shoulder and neck disability (Short et al. 1984; van Wilgen et al. 2003; van Wilgen et al. 2004; van Wilgen et al. 2004). Both strategies result in inappropriate treatment because of limitations in detecting lymph node metastasis reliably.
In addition to the nodal metastasis, many studies have also suggested that extracapsular spread (ECS) of lymph node metastasis is one of the most important negative prognostic factors for several different cancer types (Mambo and Gallager 1977; Bollen et al. 1994; van der Velden et al. 1995; Yamashita et al. 1997; Ueno et al. 1998; Tachikawa et al. 1999; Lerut et al. 2003; Nakamura et al. 2005), including head and neck cancers (Johnson et al. 1981; Carter et al. 1985; Johnson et al. 1985; Snyderman et al. 1985; Hirabayashi et al. 1991; Leemans et al. 1993; Alvi and Johnson 1996; Brasilino de Carvalho 1998; Myers et al. 2001; Greenberg et al. 2003). The detection of ECS is currently done by histological examination of the dissected lymph nodes, which is also prone to the same limitations as for the current methods of nodal metastasis diagnosis. These point to the immediate needs for new diagnostic strategies.
Currently, no molecular biomarkers have been included in clinical work-up strategies for the detection of nodal metastasis and ECS. Since several genes have been reported in retrospective trials to yield prognostic information independently of the TMN classification, it is reasonable to hypothesize that molecular “fingerprints” could exist that might define sub-groups of patients with significantly more aggressive disease. The tumor cells may progress via the bloodstream or the lymphatics to colonize new areas of the body. Gene expression signatures of the primary tumor have been identified in several tumor types for increased risk of metastasis (van't Veer et al. 2002; Kikuchi et al. 2003; Ramaswamy et al. 2003; Weiss et al. 2003; Bertucci et al. 2004; Nakamura et al. 2004; Jones et al. 2005; Xi et al. 2005). The metastasis of the HNSCCs is unique in that they metastasize mainly to regional lymph nodes through the draining lymphatics, where metastasis to distant site is relatively uncommon. Several recent gene expression studies that suggested the existence of such “fingerprints” in the primary tumor for metastasis of head and neck cancer (Schmalbach et al. 2004; O'Donnell et al. 2005; Roepman et al. 2005). In this study, we carried out the genome-wide expression analysis to identify these “fingerprints” for nodal metastasis as well as ECS and further validated them using real-time quantitative RT-PCR. Transcriptional profiling capable of predicting ECS phenotype has not been reported previously.